Audio and video disc playback systems of the type using a disc having recorded information signal encoded into a fine spiral groove typically utilize a stylus to read the encoded information signals. Included in such systems are the capacitive playback systems, wherein the stylus dielectric material is coated on at least one surface with a conductive metal layer which interacts with the conductive disc to read the information encoded thereon. An example of such a system is disclosed in U.S. Pat. No. 3,842,194 issued Oct. 15, 1974 to Clemens. Clemens discloses a video disc having a playback system utilizing variable capacitance. In one configuration of the Clemen's system informalion representative of recorded picture and sound is encoded in the form of a relief pattern in a relatively fine spiral groove on the surface of a disc record. For example, groove widths of about 3.5 micrometers and groove depths of about 1.0 micrometer may be used. During playback a pickup stylus about 2.0 micrometers wide having a thin conductive electrode thereon, for example about 0.2 micrometer thick, engages the groove as the record is rotated by a supportive turntable. Capacitive variations between the stylus electrode and the disc record surface are sensed to recover the pre-recorded information. In systems of the above type, the use of a relatively fine record groove and the requirements for a groove engaging pickup stylus result in a stylus tip which is extremely small.
During the manufacturing of such styli frequent inspection of the tip is necessary. This inspection is usually done by examination through a high power optical microscope having, for example 1000.times. to 1500.times. magnification. At such high magnification the field of view of the microscope is relatively small making the task of positioning the stylus tip tedious. Precision tooling used to hold and position the stylus during the manufacturing process generally provide banking surfaces that establish a datum and aid in the accurate positioning of the tip for inspection purposes. However, once the stylus is assembled into the stylus holder and into the cartridge such banking surfaces are no longer available.
In order to examine the stylus tip with a microscope once the stylus is in the cartridge, the tip must be aligned by reference to the stylus only. One system for doing this is disclosed in U.S. Pat. No. 4,341,472 issued July 27, 1982 to Goroy et al. There, a pair of linear arrays of photodetectors are arranged to receive projected optical images of the stylus point from both the x and y axes. Output signals from the linear arrays indicate when the stylus point is in a desired location.
Systems such as that disclosed by Goroy et al. are relatively complex and costly. The present invention, on the other hand, provides a novel mechanical apparatus for rapidly and automatically positioning a stylus tip within the field of view of a microscope without physical contact between the stylus tip and the apparatus.